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Simple Interest Calculator

Calculate simple interest on a principal for any rate and period in years, months or days.

  1. Enter your numbers
  2. Results update as you type
  3. Copy the answer or share the link
Runs in your browser. Your data and files never leave your device.

About the Simple Interest Calculator

Simple interest is charged or earned only on the original principal. It’s used for some short-term loans, bonds and term deposits that pay interest out rather than reinvesting it.

Simple Interest Calculator formula

I = P × r × t

P is the principal, r the annual rate as a decimal, and t the time in years.

Example

$5,000 at 4.5% for 3 years earns 5,000 × 0.045 × 3 = $675.

Frequently asked questions

How are days converted to years?

This calculator divides by 365. Some lenders use a 360-day year, which gives slightly more interest.

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